Bet Sizing

When it comes to betting on football games there are many systems out there. The most popular systems seem to follow the same basic idea. It goes along the idea of raising your bets when you’re winning and lowering them when you’re losing. That way you take full advantage of winning steaks and don’t get hurt on losing steaks. The reasoning behind this seems logical enough. That certainly sounds like good advice, but is it? It’s very bad advice actually. Before we get into the nuts and bolts of it, I have a simple question. How in the world does someone know they’re in the middle of a winning streak? And if they know that they’re in the middle of a steak, why wouldn’t they bet everything they have on the next game? After all, they would know they’re going to win the next game, because being in the “middle” of a winning streak means just that. That they’re going to win some more games in a row. The advice is silly on its face. As it turns out, that piece of advice has hurt far more gamblers than it’s helped. Raising and lowering your bet sizes actually makes it harder for you to win.

 

Here’s an example. Take any series of 10 bets with 5 wins and 5 losses. If you bet the same amount on every game, you’re going to break even, no surprise there. Now let’s look at a sequence of bets, raising and lowering after a win or loss. It doesn’t matter what the order is for these 5 wins and 5 losses. I’ll do two below. The one on the left is 5 wins followed by 5 losses. On the right, 5 losses followed by 5 winning bets. The bet size will be 10% of the total bankroll after the last bet. The bankroll stars out at $1000.

 

	Bet size	Bankroll			Bet size	Bankroll
		1000				1000
win	100	1100		loss	100	900
win	110	1210		loss	90	810
win	121	1331		loss	81	729
win	133	1464		loss	73	656
win	146	1610		loss	66	590
loss	161	1449		win	59	649
loss	145	1304		win	65	714
loss	130	1174		win	71	785
loss	117	1057		win	79	864
loss	106	951		win	86	950

 

The first thing we notice is that both sequences end up losing money. Remember, when you bet the same amount on each game you start with $1000 and after 5 wins and 5 losses you still have $1000. When you change bet sizes, you end up with about $950. You’ve lost about $50 in both examples, picking the same games at the same win rate, 50%. The wins and losses can be in any order. As long as there are 5 wins and 5 losses the results will be the same, minus about $50. The second thing to notice is that when you juggle the bet sizes, you have to win at a higher percentage rate to make money. Where 50% was break even, when varying bet sizes it’s a higher number.

Notice that the vig wasn't accounted for in these examples, so in real world application your money goes even faster! There’s no doubt about it, raising and lowering your bet sizes makes it harder for you win money.

This doesn’t mean to never raise your bet or lower it. If you use a bankroll, my advice is to only change your bet size at the beginning of the season and keep it at that level for the whole season.  If you don’t use a bankroll, and you should, you should never change your bet size during a season.

Most gamblers don’t understand this concept and consequently make it harder on themselves to win. Don’t fall into this trap!